The sides of the pillars are of unequal dimensions, to prove which, we shall give the measurement of two, extracted from the Letters on Iceland, containing Dr. Von TroiPs communication on this sub ject.
One with four sides.
Ft. in.
First side 1 5 Second 1 1 Third 1 6 Fourth 1 1 With seven sides Ft. In.
First side 2 10 Second b 2 4 Third 1 10 Fourth 2 0 Fifth 1 1 Sixth 1 1 Seventh 1 3 The angles are as sharp and well de fined as those of the pillars of the Giant's Causeway in Ireland, and their colour is generally black, the inclination to yellow being confined to the external sides, which are exposed to, and in some de gree bleached by, the action of the sun, rain, and wind. The texture of their substance much resembles, and is proba bly he same as the Icelandic agate. Pro fessor Bergman was divided in opinion, whether these pillars were produced by first acting upon particular substances, or whether subterraneous fires, sending forth vapour, may have softened the au penncumbent earth, which becoming soft, and yielding to the force below, as cended in this peculiar form, and became gradually petrified. This latter suppo sition met the ideas of Von Troil, who illustrates it by saying, he has observed the distinct and regular appearance allud ed to in dried clay, and even starch, when dried in a basin. " For," adds
the latter, " it may be demonstated, that they are not crystals formed by nature, by their not being produced, as all other crystals are, by external apposition (per appositionem,) nor in any other matrix, as is common among crystals." lie fur ther observes, " The following may, however, serve as a proof that I did not, without due foundation, believe them to be a kind of lava, which burst in growing cold and hard. First, you find both in the Island of Staffa, and many other places, that the pillars stand on lava or tufa, and are surrounded by this matter. Second ly, at Staffa there was a large stratum above the pillars, in which there were many pieces of those pillars irregularly thrown one among another, which leaves us to conjecture that they must have been more in number, and higher, after an old eruption of fire ; but that a subsequent eruption had overthrown them, and mix ed them with the whole mass."